Paul vowed to keep talking until the White House clarified whether it has authority to kill U.S. citizens on American soil with drones.

Administration lawyers said in all but the most extreme cases, the answer is no. Paul finally stood down, but the debate over drones is far from over.

Hypothetical Situations

Paul says a letter from the Obama administration is what set him off on the epic talking spree.

"When the president responds that, I haven't killed any Americans yet at home and that I don't intend to do so, but I might, it's incredibly alarming, and really goes against his oath of office," Paul said.

Paul mused for hours about what kinds of circumstances might prompt the White House to unleash drones on Americans and what kinds of Americans might be targeted.

"It's one thing if you want to try her for treason, but are you just going to drop a drone Hellfire missile on Jane Fonda? Are you going to drop a Hellfire missile on those at Kent State?" Rand asked.

Defining The Threat

Rand's hypotheticals verged on the outlandish, says Steve Vladeck, a law professor at American University.

"I think the Obama administration has been quite clear it would never ever use that authority except in an extreme emergency situation, the likes of which are not that hard to figure out," Vladeck says.

They would be emergencies like another Sept. 11, when terrorists hijacked a plane full of civilians and the Bush White House ordered the plane shot down anyway. Or Pearl Harbor, where enemy fliers are dropping bombs on U.S. military installations.

Republican Sen. John McCain of Arizona famously has no quarter with Fonda. She visited North Vietnam while McCain was a prisoner of war there. But McCain says the U.S. is in a different kind of war now.

"We've done, I think, a disservice to a lot of Americans by making them believe that somehow they're in danger from their government," he said. "They're not. But we are in danger. We are in danger from a dedicated enemy that is hell-bent on our destruction."

Republican Sen. Ted Cruz of Texas, who read tweets calling on Americans to #StandbyRand during the filibuster, posed this hypothetical to Attorney General Eric Holder at a hearing this week:

"If an individual is sitting quietly at a cafe in the United States, in your legal judgment, does the Constitution allow a U.S. citizen on U.S. soil to be killed by a drone?" Cruz asked Holder.

"For sitting in a cafe and having a cup of coffee?" Holder asked.

"If that individual is not posing an imminent and immediate threat of death or bodily harm, does the Constitution allow a drone to kill that individual?" Cruz replied.

"On the basis of what you said, I don't think you can arrest that person," Holder said.

Holder went on to say that in Yemen and Afghanistan, it can be difficult for the U.S. military to capture enemy combatants — not a factor for most people drinking coffee on American soil.

Drones Overseas

Democrats and Republicans on Capitol Hill have united on one issue, though: The failure of the Obama administration to release secret legal memos that explain when the U.S. government can carry out drone attacks overseas.

Vermont Democrat Sen. Patrick Leahy — chairman of the Senate Judiciary Committee — said he voted against the president's choice to lead the CIA for that reason.

And Sen. Richard Durbin, a Democrat from Illinois, says he'll hold a hearing in early April to explore the legal authority for drone strikes and what protections exist for American citizens on White House target lists.

Copyright 2017 NPR. To see more, visit http://www.npr.org/.

RACHEL MARTIN, HOST:

This is WEEKEND EDITION, from NPR News. I'm Rachel Martin. This past week, Republican Sen. Rand Paul, of Kentucky, kicked off a national conversation about drones with his 13-hour filibuster of President Obama's nominee to lead the CIA, John Brennan.

(SOUNDBITE OF SENATE FILIBUSTER)

SEN. RAND PAUL: I rise today to begin to filibuster John Brennan's nomination for the CIA.

MARTIN: For years, the Obama administration's use of drone strikes has been an open secret. That's also true for the Bush administration. But last spring, Brennan, then President Obama's counterterrorism adviser, publicly defended the use of drones. It was the first formal acknowledgment of the program.

(SOUNDBITE OF ARCHIVED RECORDING)

JOHN BRENNAN: So let me say it as simply as I can. Yes, in full accordance with the law - and in order to prevent terrorist attacks on the United States, and to save American lives - the United States government conducts targeted strikes against specific al-Qaida terrorists; sometimes using remotely piloted aircraft, often referred to publicly as drones.

MARTIN: The president's power to order drone strikes still raises concerns and misgivings from Republicans and Democrats.

PAUL: When I asked the president can you kill an American on American soil, it should have been an easy answer. It's an easy question.

MARTIN: The White House finally did answer Sen. Paul's question. Administration lawyers said in all but the most extreme cases, the answer is no - and Paul stood down.

PAUL: I thank you very much for the forbearance, and I yield the floor.

(APPLAUSE)

MARTIN: But as NPR's Carrie Johnson reports, the debate over drones is far from over.

CARRIE JOHNSON, BYLINE: Sen. Paul says a letter from the Obama administration is what set him off on the epic talking spree.

PAUL: When the president responds that, "I haven't killed any Americans yet at home," and that "I don't intend to do so, but I might," it's incredibly alarming and really, goes against his oath of office.

JOHNSON: Paul mused for hours about what kinds of circumstances might prompt the White House to unleash drones on Americans, and what kinds of Americans might be targeted.

PAUL: It's one thing if you want to try her for treason, but are you just going to drop a drone Hellfire missile on Jane Fonda? Are you going to drop a Hellfire missile on those at Kent State?

STEVE VLADECK: With all due respect to the junior senator from Kentucky, I don't think drone strikes in the U.S., against U.S. citizens, is the real issue here.

JOHNSON: That's Steve Vladeck, a law professor at American University. Vladeck told members of the Federalist Society, a conservative legal group, that the senator's hypotheticals verged on the outlandish.

VLADECK: I think the Obama administration has been quite clear that it would never, ever use that authority except in an extreme emergency situation, the likes of which are not that hard to figure out.

JOHNSON: Emergencies like another 9/11, when terrorists hijacked a plane full of civilians - and the Bush White House ordered the plane shot down anyway; or Pearl Harbor, where enemy fliers are dropping bombs on U.S. military installations. Rand Paul's Senate colleague John McCain famously has no quarter with Jane Fonda. She visited North Vietnam while McCain was a prisoner of war there. But McCain says the U.S. is in a different kind of war now.

SEN. JOHN MCCAIN: We've done a - I think a disservice to a lot of Americans by making them believe that somehow, they're in danger from their government. They are not. But we are in danger. We are in danger from a dedicated enemy that is hell-bent on our destruction.

JOHNSON: Stop talking about Jane Fonda, McCain advised, and start thinking about al-Qaida. Republican Sen. Ted Cruz of Texas - who read tweets calling on Americans to, quote, "stand by Rand" during the filibuster - posed this hypothetical to the attorney general, at a hearing this week.

SEN. TED CRUZ: If an individual is sitting quietly at a cafe in the United States, in your legal judgment, does the Constitution allow a U.S. citizen, on U.S. soil, to be killed by a drone?

ATTORNEY GENERAL ERIC HOLDER: For sitting in a cafe and having a cup of coffee?

CRUZ: If that individual is not posing an imminent and immediate threat of death or bodily harm, does the Constitution allow a drone to kill that individual?

HOLDER: On the basis of what you said, I don't think you can arrest that person.

JOHNSON: Attorney General Eric Holder went on to say that in Yemen and Afghanistan, it can be difficult for the U.S. military to capture enemy combatants - not a factor for most people drinking coffee on American soil. Democrats and Republican on Capitol Hill have united on one issue though: the failure of the Obama administration to release secret legal memos that explain when the U.S. government can carry out drone attacks overseas.

Vermont Democrat Patrick Leahy, chairman of the Senate Judiciary Committee, said he voted against the president's choice to lead the CIA for that reason. And Sen. Richard Durbin, a Democrat from Illinois, says he'll hold a hearing in early April to explore the legal authority for drone strikes, and what protections exist for American citizens on White House target lists. Carrie Johnson, NPR News, Washington. Transcript provided by NPR, Copyright NPR.